Metastable eutectic equilibrium brought down to Earth



Thermodynamic equilibrium feels comfortable because it satisfies our desire for order. For kinetic reasons, this ideal state is rarely established. Equilibrium describes the state of a system, but not how it got there. Still, we accept that metamorphic reactions will not occur at the P-T conditions predicted by the experimentally determined phase equilibria stability curves. Instead such reactions require metamorphic overstepping to provide the driving force to adjust the mineralogy to the new P-T conditions.